1. Field of the Invention
The present invention relates to a receiver, method thereof, program thereof, recording medium recording the program, and communication system, which receive plural sets of data into which plural different data items are divided, in the form of electric waves having different frequency bands, from a ground station and plural artificial satellites, appropriately demodulate the sets of data, to obtain predetermined sets of data and plural data items included in the sets of data.
2. Description of Related Art
Conventionally known digital broadcasting which provides a large number of music programs is, for example, a digital broadcasting system constructed by XM SATELLITE RADIO COMPANY, i.e., so-called XM digital broadcasting. In the XM digital broadcasting, total 100 programs to be provided are divided into two sets each including 50 programs to reduce loads to outputs of electric waves and to reduce loads to programs to be obtained. Also, in the XM digital broadcasting, ground stations each settled on the ground and two artificial satellites output electric waves in respectively different frequency bands between the two sets each including 50 programs. The total 100 programs are thus provided.
That is, in the XM digital broadcasting, electric waves are outputted from the ground stations and artificial satellites so that the programs can be received in not only city areas but also suburbs. Also, in the XM digital broadcasting, the electric waves of different frequency bands which respectively differ between the sets each including 50 programs are outputted from each of the two artificial satellites, so that even a moving object which is moving like a vehicle can receive the programs. This is because the electric waves from one artificial satellite can be securely received even if the electric waves from the other satellite come to be not received due to movement of a moving object. Thus, in the XM digital broadcasting, the electric waves in different frequency bands which differ respectively between the sets of programs are outputted from each of two artificial satellites and one ground station. Electric waves in total 6 kinds of frequency band are used.
Also, the XM digital broadcasting adopts a structure in which electric waves of three kinds of the set including a desired program to be obtained are received, among the outputted electric waves of the total six kinds of frequency band, in order to obtain the desired program. To switch the program to be obtained to another program, for example, there is a method of directly selecting another program by operating a button. There may be another method of, for example, as shown in FIG. 14, selecting another program by continuously changing programs until a favorite program is found out, in consideration of the large number of programs provided. Alternatively, there is another method of sequentially outputting programs each for a predetermined time period until the same genre as that immediately before starting switching the program is selected.
When a program which has been being obtained is switched to another program, there is a case that the another program belongs to the other set of programs than the set of programs to which the foregoing program belongs. In this case, it is necessary to receive electric waves of the other three kinds of frequency band, which correspond to the other set of programs. Further, electric waves are received with a time delay for four seconds or so maintained between the two artificial satellites, due to the positional relationship between the artificial satellites and the like. That is, there is a time interleaf between the two artificial satellites. Suppose hence that programs are switched by shifting programs forwardly as shown in FIG. 14, in case of a program configuration as shown in FIG. 5, for example. As shown in FIG. 15, two seconds or so are required until another program in the same set is outputted. However, six seconds or so are required if a program is switched to another program in the other set and if only one electric wave can be received from satellites. Therefore, every time when a program is switched to another program in a different set of programs, a long time is required before the another program is outputted. Utility is thus not improved.
It may be possible to eliminate the drawback of the time interleaf by attaining all of the electric waves of the six kinds of frequency bands equivalent to the two sets of programs. In such a structure, the number of programs increases several times, enhancing the data amount outputted in the form of electric waves. Consequently, processing loads are increased so that the size and power consumption of the device may increase.